Radome

ABSTRACT

Embodiments of the present disclosure provide a cover for an antenna for electromagnetic radiation of a specific wavelength. The antenna includes an array of radiating elements, such as a plurality of horn antennas. The cover comprises a layer of cellular embossments, an upper side, and a lower side. The distance between the upper side and the lower side is approximately ¼ of the wavelength. The upper side of the layer comprises the area within an upper side of the embossments, the lower side of the layer comprises the area surrounding the embossments, and the lower side of the layer is arranged in a spaced relationship from the antenna in a radiating direction of the antenna. The antenna is mounted on a portable satellite terminal operating in the X band.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of prior GermanPatent Application No. 10 2016 101 583.0, filed on Jan. 29, 2016, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a cover for an antenna, in particularfor antenna systems for mobile satellite communication.

BACKGROUND

Antennas for use under hostile environmental conditions, as is the casewith antenna systems in mobile satellite communication, should becovered to prevent soiling or damage, regardless of whether they areportable or mounted on aircraft or other vehicles.

German patent document DE 10 2010 019 081 A1 shows an antenna designedas an array of horn antennas.

Depending on how the antenna is used, the range of conditions concerningwhich protection is required can include humidity, rain, sand, dust,chemicals, lightning, collisions with birds (in the case of airplanes)and many more. The electrical or high-frequency performance capacity ofthe radome (i.e. the cover or structure protecting the antenna) of theantenna is also important. This is indicated by electrical losses andsuppression of cross-polarization.

The electrical losses are both reflective and dissipative in nature.Whereas the dissipative losses arise from the dielectric properties ofthe materials used, the reflections are defined by the quality of thehigh-frequency design. A skillful selection of materials, geometries andstructures can minimize the reflective losses for the desired area ofuse and frequency range.

According to the state of the art, multi-layer sandwich structures ofdifferent composite and similar materials may be selected for a cover(i.e. a radome) for antennas.

DE 199 02 511 A1 discloses a basic design and function of a cover forantennas. A conventional sandwich-type radome has three interconnectedlayers: an inner liner, a radome core (having a thickness equal to ¼ ofthe wavelength, smallest possible dielectric constant) and an outerlining. In the case of two reflective layers spaced apart one behind theother at a distance of ¼ of the wavelength, the two resultingsub-reflections cancel each other out, since the phase difference of thetwo sub-waves equals 2*¼ of the wavelength, i.e. 180°. This keeps thereflections of the wave at the cover at a low level. Manufacturing theseradomes requires a corresponding knowledge of adhesion, laminating andcomposite techniques, and also a well-balanced selection of thedifferent materials.

In some applications, such as in airplanes, the radome is curved toimprove the aerodynamic properties of the antenna mounted on thefuselage. For example, WO 2014/005691 A1 discloses that a radome (i.e.the cover of an antenna) can display polarization isotropy due to acurvature, which can result in marked changes in the axial ratio ofcircularly polarized signals passing through the radome. DE 10 2010 019081 A1 discloses a radome that has been aerodynamically optimized.

United States Patent Application No. 2010/0309089 A1 discloses anantenna with several dipole elements. The dipole elements are providedwith a cover that has a honeycomb structure, thereby forming partitionsbetween the dipole elements and an individual radome for each dipoleelement.

SUMMARY

Embodiments of the present disclosure provide a simplified structure foran antenna cover, relative to a sandwich-type cover design.

According to embodiments of the present disclosure, a cover of anantenna for electromagnetic radiation of a specific wavelength comprisesa layer with uniformly arranged cellular embossments. When viewed froman upper side or lower side of the layer, the layer within an embossmentis spaced apart from the layer outside of the embossment by a distancethat corresponds to approximately ¼ of the wavelength of the antennasignals. The cover and hence also the underside of the layer are latermounted in the direction of radiation of the antenna and in spacedrelationship to the antenna, thereby forming a radome for the antenna.

According to embodiments of the present disclosure, a cover of anantenna for electromagnetic radiation of a wavelength is provided. Thecover comprises a layer comprising a plurality of cellular embossments,an upper side, and a lower side, with a distance between the upper sideand the lower side being approximately ¼ of the wavelength, wherein theupper side of the layer comprises an area within an upper side of theembossments, the lower side of the layer comprises an area surroundingthe embossments, and the lower side of the layer is arranged in a spacedrelationship from the antenna in a radiating direction of the antenna.

According to embodiments of the present disclosure, an antenna forsatellite communication is provided. The antenna comprises an array ofradiating elements and a cover configured sealing the array. The covercomprises a plurality of cellular embossments, an upper side, and alower side, a distance between the upper side and the lower side beingapproximately ¼ of the wavelength of the antenna, wherein the upper sideof the cover comprises the area within an upper side of the embossments,the lower side of the cover comprises the area surrounding theembossments. The cover is mounted on the antenna such that the lowerside of the cover is spaced in relation to the array of radiatingelements.

According to embodiments of the present disclosure, a cover of anantenna for electromagnetic radiation of a wavelength is provided. Thecover comprises a layer defining a continuous surface, the layercomprising a plurality of cellular embossments, an upper side, and alower side arranged parallel to the upper side, a depth of theembossments corresponding to a distance between the upper side and thelower side, and lateral supports configured to separate the lower sideof the layer from the antenna, wherein an upper side of the embossmentsdefines the upper side of the layer, the area surrounding theembossments defines the lower side of the layer, and the distancebetween the upper side and lower side is substantially equal to ¼ of thewavelength.

According to embodiments of the present disclosure, in the radiatingdirection of the antenna, i.e. orthogonally to the aperture of theantenna, the layer has cellular embossments with different contours.Depending on the shape of the embossments, different views of theembossments generally appear from the two sides of the layer. However,it is also contemplated that identical views of the cover are generatedif the embossments are precisely square and diagonally arranged or ifthey are tapered.

According to embodiments of the present disclosure, the embossments mayform a type of pseudo-three-layer structure using only one layer ofmaterial. The pseudo-three-layer structure includes a pseudo-inner layerand a pseudo-outer layer. Due to the embossments, the pseudo-inner layerand pseudo-outer layer may each have a lower effective dielectricconstant than a solid material. This may improve the degree andachievable bandwidth of the reflection suppression. The depth of theembossments or the spacing of the pseudo-inner/outer layers (forexample, as in the conventional sandwich radome) may be set atapproximately ¼ of the wavelength to minimize reflections. The cover canbe operated bidirectionally. For example, the lower side or the upperside of the cover can face the antenna aperture or similarly slightreflections can be achieved for transmitting and receiving operations.

According to embodiments of the present disclosure, the cover may bespaced slightly apart from the surface of the antenna. For example, thelower side of the cover may arranged such that the lower side does notlie directly on the antenna, but rather is spaced so that the emittedwave of the antenna is substantially plane in the area of the cover. Forexample, this may be achieved by spacing the cover and the surface ofthe antenna by about ¼ of the antenna wavelength.

According to embodiments of the present disclosure, a polarizationfilter may be placed between the antenna and the cover thus constitutinga polarization layer. The hollow space between the antenna and the covermay accordingly be larger to accommodate the polarization filter. Forexample, the distance may be at least ½ of the antenna wavelength.

According to embodiments of the present disclosure, the cover mayprotrude beyond the antenna in the x and y directions to avoiddistortion at the edges of the antenna. For example, these distortionsmay become negligible with a protrusion of as little as approximatelyone wavelength.

According to embodiments of the present disclosure, the upper side maybe separated from the lower side of the layer by less than ¼ of thewavelength. Thus, the layer may be very thin. For example, the thicknessof the layer may be between 0.5 and 3 mm. The thickness of the layer isselected for a desired balance between mechanical stability (i.e. usingas thick a layer as possible) and low dissipative losses or superimposedreflections on the lower and the upper sides of the layer (i.e. using asthin a layer as possible).

According to embodiments of the present disclosure, the embossments maybe symmetrically shaped in the x and y directions of the upper and lowersides, and/or are mutually arranged so as to yield a symmetricaldistribution of the embossments in the x and y directions of the upperand/or lower sides. Thus, the cover may also be suitable forelectromagnetic radiation of circular polarization. In circularpolarization, both orthogonal field components must be treatedidentically, as undesirable cross-polarization effects may otherwiseoccur. For purely linear polarizations, asymmetrical (e.g., rectangular)embossments or groups of embossments may be used.

According to embodiments of the present disclosure, the area sums of theupper sides and the area sums of the lower sides of the layer may beapproximately equal. Therefore, the signal intensities reflected insideand outside the embossments are approximately equal, which optimizes thecancellation effect.

According to embodiments of the present disclosure, to keep the layer asthin as possible while maintaining a large degree of stability, at leastone reinforcement around the embossment may be provided, between theupper and the lower sides, in addition to the side walls. Thisreinforcement connects both the upper and the lowers side between twoembossments. The reinforcement may be wider at a transitional area fromthe reinforcement to a side wall of the embossment. This may make iteasier to mill the cover through the curves and may improve thedissipation of force between the embossments. Alternative manufacturingprocesses for the cover may include deep-drawing, injection molding or3D printing. The side walls between the upper and the lower sides may beslightly tapered for this purpose.

According to embodiments of the present disclosure, at least onereinforcement is arranged around the embossment. The reinforcement mayconnect two adjacent embossments at the upper side and the lower side ofthe layer. The reinforcement may also comprise a protrusion, such thatthe reinforcement has a width at the embossment that is greater than adistance of the protrusion from the embossment.

According to embodiments of the present disclosure, the cover may beused for an antenna system comprising an array of horn antennas. Auniform arrangement of the embossments may be used for this purpose.Embossments and horn antennas can then be oriented to one anotheraccordingly. A reinforcement or a side wall may be arranged at a centerof a horn antenna to orient the radiation pattern of the horn antennatoward its center. A reinforcement or side wall may contain a largervolume of the material of the layer. As an alternative, a point (e.g. acenter point) of the layer between embossments that are adjacent in thex and y directions is oriented to the center of the horn antenna.

According to embodiments of the present disclosure, the dimensions ofthe embossment in the x and y directions can be selected to represent adesired compromise between electrical performance and mechanicalstability. For example, larger dimensions of the embossment may providea lower effective dielectric constant of a pseudo-core of the embossment(i.e. the hollow space within the embossment), lower reflections, and alower weight. The structure may also be more fragile structure at somepoint in time.

According to embodiments of the present disclosure, a compromise betweenmechanical stability and high electrical performance can be reachedthrough appropriate mechanical reinforcements. For example, the radomemay use hexagonal shapes similar to those found in honeycombs or shapessimilar to those found in egg cartons to achieve a high mechanicalstability at a light weight.

According to embodiments of the present disclosure, a dimension of ahorn antenna in the x and y directions may be equal to, a multiple of,or an even fraction of a cellular embossment to minimize reflections onthe cover across the entire horn antenna array and to distributereflections evenly.

According to embodiments of the present disclosure, the embossments maybe substantially square. The embossments may also haveproduction-related curvatures in the transitional area between the sidewall and the upper and/or lower side or between the side walls, to makeit easier to produce them by milling.

According to embodiments of the present disclosure, the layer canconsist of synthetic materials such as polypropylene, polyethylene orpolyamide, and that a material with a low dielectric constant isselected from this group of materials.

According to embodiments of the present disclosure, an antenna ismounted on a portable satellite terminal for an X band (7.25 GHz-8.40GHz). Such an antenna may include an arrangement of more than 1000embossments per square meter. For example, for the X band, this mayinclude between 1000 and 1200 embossments per square meter. For a coverthat is optimized to the center frequency of the X band, the width of anembossment may be approximately 3 cm. In an application of this type forsatellite communication the cover may be mounted onto a radiatingelement array of the antenna, such as a horn antenna array, therebyforming a seal. However, the cover can also be used for other types ofantenna. While the radome described here is optimized for portable,mobile applications in the X band, it can be rescaled for use in otherfrequency ranges.

According to embodiments of the present disclosure, a hollow spacebetween the antenna and the cover is generally filled with air. Toobtain a large degree of mechanical stability this hollow space can alsobe foamed out.

According to embodiments of the present disclosure, for portablesatellite receivers/transmitters the side walls of the cover may beperpendicular to the antenna, since there are no particular aerodynamicrequirements. In applications on aircrafts in which the cover ispositioned in the airflow, the embossments of the upper side may befilled with a material that results in a smooth surface and that has adielectric constant close to that of air.

According to embodiments of the present disclosure, the shape of thecover may be substantially plane and parallel to the antenna. For theaforementioned application on aircrafts, the cover may be bent into anaerodynamically favorable shape such as a paraboloid.

According to embodiments of the present disclosure, additionalprotection of the cover layer may be provided. For example, theadditional protection may be via a coating on the upper side of thelayer with a UV-resistant protective varnish layer with no metalparticles. The dielectric constant of the varnish should be particularlylow, for example smaller than that of the layer.

The described properties of the present disclosure and the manner inwhich these are achieved will be described in more detail based on thefollowing detailed description. The foregoing general description andthe following detailed description are exemplary and explanatory only,and are not restrictive of embodiments consistent with the presentdisclosure. Further, the accompanying drawings illustrate embodiments ofthe present disclosure, and together with the description, serve toexplain principles of the present disclosure. The accompanying drawingsshall only be regarded to be of a schematic, exemplary nature, and notas being true to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an antenna with a cover according to thepresent disclosure;

FIG. 2 is a perspective view showing details of an antenna with a coveraccording to the present disclosure;

FIG. 3 is a plan view showing structural outlines of a cover and a hornantenna array;

FIGS. 4-6 are perspective views showing various aspects of a cellularembossment of a cover;

FIGS. 7-8 are perspective views showing details of a cover with multipleembossments; and

FIG. 9 is a graph showing the reflective behavior of a cover in the Xband.

DETAILED DESCRIPTION

FIG. 1 shows a perspective view of an antenna 10 with the cover 1according to an embodiment of the present disclosure. The antenna 10includes an array 12 of radiating elements, for example, a plurality ofhorn antennas 11. The antenna 10 also includes a feed network connectingthe individual horn antennas 11 to a transmitting and receiving unit(not shown in FIG. 1).

The cover 1 is mounted to the antenna 10 such that a space greater thanor equal to ½ of the wavelength of the antenna is maintained between thecover and the antenna, and a seal is formed so that environmentalinfluences do not effect operation of the antenna 10. The cover 1 isessentially plane and consists of a layer 2 and supports 2 a. The layer2 and the supports 2 a may be made of the same material. The supports 2a separate the layer 2 from the antenna 10, align the layer 2 parallelto the radiating element array 12 and create a seal or enclosure. Thelayer 2 has a protective coating of varnish on its upper side 4 (seeFIG. 4). The layer 2 may be made of Teflon, for example.

A meander-type polarization layer 13 can be introduced into the hollowspace shown between the radiating element array 12 and the cover 1. Themeander-type polarization layer converts linear polarized waves tocircular polarized waves.

The layer 2 and the radiating element array 12 are essentially plane,but may include structures that are perpendicular to this plane. Thesestructures may be formed by milling and are shown in FIG. 2.

In FIG. 2, the horn antennas 11 of the radiating element array 12 areembodied as ridged horn antennas with an additional corrugation 16.However, other forms of horn antenna may also be used.

A ridged horn antenna is surrounded at the aperture end (i.e. towardsthe opening of the horn antenna 11 shown in FIG. 2) by a singleradiating element edge 14 that is separated from the ridged horn antennaby the corrugation 16. The single radiating element edge 14 here isconnected to a single radiating element in spaced relationship to theaperture surface.

Ridges 15 (i.e. constrictions) of the ridged horn antennas lower thecutoff frequency, so that the installation size for the frequency rangesof interest can be reduced. The corrugation 16 improves matching andreduces undesirable cross-polarization. As a result of this arrangement,a wave from the ridged horn antenna and a wave from the corrugation 16are superimposed. The corrugation 16 may be dimensioned such that a waveentering the corrugation 16 and reflected at an end of the corrugation16 is structurally superimposed by a wave emerging from the ridged hornantenna.

The single radiating element edge 14 may have a rectangular shape. Therectangular shape may include rounded corners produced via themanufacturing process. The ridged horn antenna is arranged in the centerof the rectangular-shaped single radiating element edge 14. Thus,several single radiating elements of this kind can be combined to form ahorn antenna array 12 without loss of space. A square contour of thesingle radiating element edge 14 may simplify the combined horn antennaarray in both directions. With a centered arrangement of the ridged hornantenna, the radiation pattern is oriented to the center of the singleradiating element. Considering that a slight inclination of theradiation pattern to the side of the electric field incoupling may becompensated for in the case of an electric field incoupling, thearrangement of the ridged horn antenna may also be slightly offset fromthe center.

The corrugation 16 has substantially perpendicular walls in relation tothe aperture area. The corrugation 16 opens directly to the aperturearea and avoids an inclination, which would otherwise result inincreased space requirements parallel to the aperture area.

The number of ridges required is dependent on the number ofpolarizations that are supported. The ridged horn antenna shown in FIG.2 has four ridges arranged crosswise, each of which is oriented to thecenter of the ridged horn antenna. This arrangement is generallysymmetrical, so that an angular distance between two ridges is 180° or90°. Additional details on the ridged horn antenna can be found in DE 102014 112 825 A1, the contents of which are incorporated by reference.

A possible alignment of the cover 1 over the radiating element array 12is shown in FIG. 3. The contours of embossments 3 of the cover 1 areexplained below with reference to a center 9 of the horn antenna 11. Asshown in FIG. 3, the embossments 3 are not oriented to the center 9 ofthe horn antenna 11. Rather their complement, in the form of a roundedcross, between the embossments 3 is oriented to the center 9 of the hornantenna 11. Reinforcements 8 (described below) lie over the singleradiating element edges 14. This arrangement enables the decoupling ofthe radiation pattern of adjacent horn antennas 11 while providing ahigh material density of the layer 2 at the center 9.

Alternatively, the reinforcement 8 between embossments 3 can be orientedto the center 9 of the horn antenna. Here the enhanced material densityof the cover may cause the radiation pattern of a horn antenna to beoriented to the center 9.

The cellular embossments 3 of the layer 2 are illustrated in FIGS. 4 to6. The layer 2 has an upper side 4 and a lower side 5. The layer 2 isrelatively thin, for example having a thickness of 1.2 mm, in comparisonto a depth d of layer 2, which is the distance between the upper side 4and the lower side 5 of the layer 2 through the embossment 3 (as shownin FIG. 6).

Viewed from the upper side 4 (see FIG. 4), reinforcements 8 can be seenarranged between sidewalls 7 of the embossment 3 toward adjacentembossments (not shown in FIG. 4). The sidewalls 7 are perpendicular tothe upper side 4 and the lower side 5 of the layer 2. The reinforcement8 is wider in the transitional area from the reinforcement 8 to a sidewall 7 of the embossment 3. Curvatures 6 are provided at the transitionfrom the reinforcement 8 to the side wall 7, and in the embossment 3between the side walls 7, as shown in FIG. 5.

In the embossment 3 shown in FIG. 5, the basic square shape of theembossment 3 can be more clearly seen. The upper side 4 (see FIG. 4) andthe lower side 5 (see FIG. 5) of the layer 2 are both plane butseparated by the depth (i.e. the distance d shown in FIG. 6) of theembossment 3 and the thickness of the layer 2.

FIG. 6 shows that the thickness of the layer 2 may be smaller than thedistance d from the lower side 5 of the layer 2 inside the embossment 3to the upper side 4 of the embossment 3. The thickness of the layer 2may be, for example, 1.2 mm. The distance d is determined by thewavelength of the electromagnetic radiation of the antenna. For afrequency band, for example 7.25 GHz-8.4 GHz in the X band, the centerfrequency f is selected, here f=7.825 GHz, to determine the distance d.The distance d is yielded from ¼ of the wavelength λ, thus in this cased=c/4*f approx. 1 cm, wherein c is the speed of light.

FIGS. 7 and 8 show remote views of the layer 2 with a plurality ofembossments 3, viewed from the upper side 4 (FIG. 7) and the lower side5 (FIG. 8). The embossments 3 are symmetrical in both directions ofextension x and y of the plane layer 2. The arrangement of theembossments 3 provides a distance between the cellular embossments thatremains constant across the surface in both directions x and y. Thenumber of embossments 3 per square meter may lie between 1000 and 1200,if as in the present case one embossment 3 per horn antenna 11 isselected. As an alternative, one embossment 3 can also cover 4, 9, 16,etc. horn antennas 11 or conversely, 4, 9, 16, etc. embossments 3 perhorn antenna 11 can also be provided.

Therefore, despite having only one layer 2, the antenna 10 is given avirtual multi-layer structure comprised of two portions spaced apart by¼ of the wavelength λ. The embossments 3 also include high air content(inside the embossments 3), providing an effective dielectric constantthat is lower than that of the material of the layer 2, signifying lowreflections across the bandwidth of the X band (as shown in FIG. 9, forexample).

In some embodiments of the present disclosure, the embossments 3 includedimensions such that the sum of the areas of the upper side 4 of layer 2(i.e. the upper sides as shown in FIG. 7) is equal to the sum of theareas of the lower side 5 of the layer 2 (i.e. the lower sides as shownin FIG. 8). Thus, both reflective areas have roughly the same proportionof beams reflected at the layer 2 and can cancel each other out.

FIG. 9 shows a reflectance factor r for the cover of the presentdisclosure. Reflections amount to less than −30 dB in the range of 7.25GHz to 8.4 GHz, such that that less than 0.1% of the antenna power isreflected. The reflective losses in this case are essentially zero andonly the material-dependent internal dissipative losses remain.

Embodiments of the present disclosure describe an efficient cover (i.e.radome) of an antenna for the X band that can be used for portableantennas in mobile satellite communication. For example, the antenna(10) may be mounted on a portable satellite terminal (20) for an X band.However, this cover can also be rescaled for other frequency bands inaccordance with the designated design criteria.

Having described aspects of the present disclosure in detail, it will beapparent that modifications and variations are possible withoutdeparting from the scope of aspects of the present disclosure as definedin the appended claims. As various changes could be made in the aboveconstructions, products, and methods without departing from the scope ofaspects of the present disclosure, it is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

LIST OF REFERENCE NUMBERS

-   -   cover 1    -   layer 2    -   support 2 a    -   embossments 3    -   upper side 4    -   lower side 5    -   side walls 7    -   curvature 6    -   reinforcement 8    -   center of a horn antenna 9    -   antenna 10    -   horn antenna 11    -   radiating element array 12    -   single radiating element edge 14    -   constriction 15    -   corrugation 16    -   satellite terminal 20    -   distance d    -   frequency f    -   reflectance factor r    -   wavelength λ

What is claimed is:
 1. A cover of an antenna for electromagneticradiation of a wavelength, the cover comprising: a layer comprising aplurality of cellular embossments, an upper side, and a lower side, adistance between the upper side and the lower side being approximately ¼of the wavelength; wherein: the upper side of the layer comprises thearea within an upper side of the embossments; the lower side of thelayer comprises the area surrounding the embossments; and the lower sideof the layer is arranged in a spaced relationship from the antenna in aradiating direction of the antenna.
 2. The cover according to claim 1,wherein the distance between the upper side of the layer and the lowerside of the layer is less than ¼ of the wavelength and a thickness ofthe layer is between 0.5 and 3 mm.
 3. The cover according to claim 1,wherein the layer extends in an x and y direction, and the embossmentsare symmetrically shaped in the x and y directions of the upper side ofthe layer.
 4. The cover according to claim 1, wherein the layer extendsin an x and y direction, and the embossments are arranged relative toone another so as to yield a symmetrical distribution of the embossmentsin an x and y direction of the upper side of the layer.
 5. The coveraccording to claim 1, wherein an area sum of the area within the uppersides of the embossments is approximately equal to an area sum of thearea surrounding the embossments.
 6. The cover according to claim 1,wherein the embossments comprise: side walls between the upper side andthe lower side of the layer; and at least one reinforcement arrangedaround the embossment, the reinforcement connecting two adjacentembossments at the upper side and the lower side of the layer.
 7. Thecover according to claim 6, wherein the reinforcement comprises aprotrusion, the protrusion having a width at the embossment that isgreater than a width at a distance from the embossment.
 8. The coveraccording to claim 1, wherein the antenna is a horn antenna arraycomprising a plurality of horn antennas.
 9. The cover according to claim6, wherein: the antenna is a horn antenna array comprising a pluralityof horn antennas; and a reinforcement of an embossment connects to areinforcement of an adjacent embossment at a connection point, theconnection point being oriented to a center of a horn antenna.
 10. Thecover according to claim 8, wherein the layer extends in an x and ydirection, and a dimension of the horn antenna in the x and y directionsis equal to, a multiple of, or an even fraction of a dimension of anembossment.
 11. The cover according to claim 1, wherein the embossmentsare substantially square.
 12. The cover according to claim 6, whereinthe embossments comprise curvatures in the transition between thereinforcement to the side wall or between the side walls within anembossment.
 13. The cover according to claim 1, wherein the layer isselected from the group consisting of polypropylene, polyethylene andpolyamide.
 14. The cover according to claim 1, wherein the layercomprises at least 1000 embossments per square meter.
 15. The coveraccording to claim 1, wherein the antenna operates in the X band, andthe layer comprises between 1000 and 1200 embossments per square meter.16. The cover according to claim 1, wherein the layer is substantiallyplane and comprises a protective coating.
 17. An antenna for satellitecommunication, comprising: an array of radiating elements forelectromagnetic radiation of a wavelength; and a cover configured toseal the array, the cover comprising: a plurality of cellularembossments; an upper side; and a lower side separated from the upperside in a radiating direction of the antenna by a distance ofapproximately ¼ of the wavelength.
 18. The antenna according to claim17, wherein the antenna is mounted on a portable satellite terminaloperating in the X band.
 19. A cover of an antenna for electromagneticradiation of a wavelength, the cover comprising: a cover layer defininga continuous surface, the layer comprising a plurality of cellularembossments, an upper side, and a lower side arranged parallel to theupper side, a depth of the embossments corresponding to a distancebetween the upper side and the lower side; and lateral supportsconfigured to separate the lower side of the layer from the antenna;wherein: an upper side of the embossments defines the upper side of thelayer; the area surrounding the embossments defines the lower side ofthe layer; and the distance between the upper side and lower side issubstantially equal to ¼ of the wavelength.
 20. The cover according toclaim 19, wherein the upper side of the embossments is substantiallysquare, and the embossments comprise: side walls between the upper sideof the layer and the lower side of the layer; and at least onereinforcement arranged around the embossment connecting the upper sideand the lower side of the layer between two adjacent embossments.